Melanin is a natural pigment found in hair. Melanin and hair-forming cells are naturally produced in the hair bulb at the root of the hair. As new cells are produced, the older ones are pushed upwards out of the skin to form the hair shaft, which is the part of the hair that can be seen above the scalp. Hair can be schematically described as being made of a center part called the cortex, which contains the melanin, and an outer layer called the cuticle. It is the cortex that gives the hair its special qualities such as elasticity and curl.
The hair shaft is composed of dead cells that have turned into a mixture of different forms of the hair protein, keratin. Keratin contains high concentrations of a particular amino acid called cystine. Every cystine unit contains two cysteine amino acids in different chains, which have come to lie near each other and are linked together by two sulphur atoms, forming a very strong chemical bond known as a disulphide linkage. This cross-linking by disulphide linkages between the keratin chains accounts for much of the strength of the hair.
Bleaching and dyeing (or coloring) of hair has become increasingly popular over the past years. Younger people may want to change the natural color of their hair to a more fashionable one, while older people may also use dyeing compositions to conceal gray hair. As people grow older, the production of melanin slows, giving more and more gray hair over time.
Melanin can also be purposely altered by chemical treatments to give lighter shades. The lightening is achieved by oxidizing the melanin pigments with an oxidizing composition, usually in alkaline solution. The oxidizing compositions (bleaches) comprise an oxidizing agent, usually hydrogen peroxide. Other suitable oxidizing agents include potassium, sodium and ammonium salts of perborate, percarbonate, persulfate and percarbamide.
Bleaches are also used during oxidative dyeing treatments. Oxidative (or “permanent”) dye compositions comprise “precursor dyes” which are small molecules capable of diffusing into the hair. These molecules mainly belong to three classes of aromatic compounds: diamines, aminophenols and phenols. They are sufficiently small to diffuse in the hair shaft where, once activated by an oxidizing agent such as hydrogen peroxide, they further react with other precursors to form larger colored complexes. These compounds can be used in numerous combinations in order to provide a particular desired colour. Oxidative hair dye compositions commonly contain, in addition to the dye precursors and a source of peroxide, a variety of additional cosmetic and peroxide stabilizing agents.
In order to stabilize the hydrogen peroxide solution which, even at acetic pH, has a tendency to decompose rapidly in solution thereby affecting its storage stability, low levels of chelants are routinely used as stabilizers or preservatives in various oxidizing compositions. For example, EDTA (ethylenediaminetetraacetic acid) is commonly used as a stabilizer in hydrogen peroxide solution. Amounts as low as 0.1% by weight of the oxidizing composition are usually used to stabilize the oxidizing agent contained in said oxidizing compositions.
Oxidative hair colourant treatments generally provide acceptable immediate results. However, achieving the desired tonality for oxidative colourants is still difficult. For example to provide ash or blue tones to blondes or to provide red tones to auburn and burgundy shades is still particularly difficult. Moreover, these tonal shades suffer from the additional drawbacks regarding their low root to tip evenness, as well as a tendency to rapidly lose the given tonality during subsequent wash cycles. This is due in part to a combination of factors; namely that firstly the dyes typically providing the tonality are only used at low levels in comparison to the other dye levels used to provide a particular shade; secondly that these dyes also have a low initial uptake in the hair and thirdly that these dyes also tend to have a rapid wash fade profile.
It has now been surprisingly found that chelants having an amino-phosphonic moiety, in particular in combination with selected oxidative couplers improve the tonality delivered by these dyes. It is a further advantage of the present invention that the initial dye uptake and wash fade is also improved. Whilst not being bound by theory, it is believed that the improved tonality is due to the ability of the amino-phosphonate type chelants to be effective chelators in both the oxidised and non oxidised form.
Phosphonate type chelants have been described in the art. U.S. Pat. No. 4,138,478 discloses agents for reducing the damage to hair during bleaching and dyeing by the use of a water-soluble 3-amino-1-hydroxypropane-1,1-diphosphonic compound to protect the hair from damage by “nascent oxygen”. Other protective compounds such as hydroxyethane-1,1 diphosphonic acid (HEDP) and ethylenediaminetetramethylene phosphonic acid (EDTMP) are disclosed at low levels in U.S. Pat. No. 3,202,579 and U.S. Pat. No. 3,542,918.
U.S. Pat. No. 3,542,918 describes certain phosphonates for the prevention of damage to hair upon dyeing. A dye cream (“based upon conventional oxidative dyes”) and phosphates is disclosed. WO02078661 also describes oxidising compositions comprising a phosphonic acid type chelant and a conditioning agent for improved hair feel. WO98/27944 describes hair colouring compositions comprising oxidising agent and hair colouring agent having a pH of from 1 to 4.5 to provide colour, good wash fastness and reduced hair damage. Chelants are disclosed. U.S. Pat. No. 5,635,167 describes the removal of minerals from hair by the application of a chelating agent selected from amino acid type or polyphosphate or phosphonate type agents.